This invention relates to an improvement of a damping force generator in a hydraulic damper used for an automobile suspension or the like.
Conventional damping force generators for hydraulic dampers used in an automobile suspension are, for example, disclosed in Tokkai Hei 1-111840 or Tokkai Hei 2-93136.
FIG. 11 and FIG. 12 show a damping force generator in a hydraulic damper disclosed in Tokkai Hei 1-111840.
As shown in FIG. 11, this hydraulic damper comprises an outer tube 1 and an inner tube 2 coaxially housed in the outer tube 1. A piston 3 is housed in the inner tube 2. The interior of the inner tube 2 is divided by this piston 3 into an oil chamber 8 on the rod side and an oil chamber 9 on the piston side, each of these oil chambers being filled with a hydraulic fluid. A tank chamber 10 is formed between the outer circumference of the inner tube 2 and the inner circumference of the outer tube 1, this tank chamber 10 being filled with the hydraulic fluid and air.
The piston 3 is penetrated with a plurality of outer throughholes 11 and inner throughholes 12. A check valve 19 provided at the upper end of the outer throughholes 11 is pushed open when a piston rod 4 connected to the piston 3 moves in the compression direction, and hydraulic fluid flows from the oil chamber 9 to the oil chamber 8. On the other hand, when the piston rod 4 moves in the extension direction, a piston valve 20 provided at the lower end of the inner throughholes 12 is pushed open, hydraulic fluid flows from the oil chamber 8 on the rod side to the oil chamber 9 on the piston side, and an extension damping force is generated due to resistance to this flow.
A base valve unit 15 is mounted at the lower end of the inner tube 2. When the piston rod 4 moves in the compression direction, hydraulic fluid having a volume equivalent to that of the piston rod 4 inside the inner tube 2 flows into the tank chamber 10 and is absorbed. This hydraulic fluid flows via a base valve 15A in the base valve unit 15, and the base valve 15 A generates a compression damping force due to this flow.
As shown in FIG. 12, the piston valve 20 comprises a main leaf valve 21 and a sub-leaf valve 22 which are laminated on each other such that the damping force can be varied in two steps. Describing this in further detail, the main leaf valve 21 has an outer circumferential edge portion which is brought in contact with a seat surface 16 so as to seal a port 17 of the inner throughholes 12 formed in a base 3A of the piston 3. The sub-leaf valve 22 is disposed below the main valve 21 and adheres to it, and closes an opening 21A formed in the main leaf valve 21. Hence, when the extension speed of the piston rod 4 is small and the pressure differential between the oil chamber 8 and the oil chamber 9 is small, only the sub-leaf valve 22 is pushed open due to its low bending rigidity. Thus a minute damping force with a good response is generated as an extension damping due to the opening 21A. On the other hand, when the extension speed of the piston rod 4 rises, and the oil pressure in the oil chamber 8 rises, the main leaf valve 21 is pushed open, hydraulic fluid flows between the outer circumferential edge portion of the main leaf valve 21 and the sheet face 16, and increase of the extension damping force is suppressed so that the damping is gradual.
However, in such a damping force generator for a hydraulic damper, when the extension speed of the piston rod is high, the effective diameter of the main valve 21 (diameter of the seat surface 16) must be sufficiently increased and its deformation made easier so that any increase of extension damping force generated by the piston valve 20 is smooth.
However when the piston rod moves in the compression direction and oil pressure acts from the side of the oil chamber 9 on the main leaf valve 21 of which the diameter has been increased in this way, the valve 21 severely bends toward the port 17. This causes a gap to form with the sub-leaf valve 22 so that hydraulic oil flows from the opening 21A, and there is a possibility that fatigue may occur due to increase of bending stress. This problem is particularly evident when back throttling is performed wherein the hydraulic oil flowing through the outer throughholes 11 is throttled so as to generate a part of the compression damping force and the piston rod moves in the compression direction.
This invention, which was conceived in view of the above problems, aims to provide a damping force generator for a hydraulic damper in which the valve that generates damping force is protected from pressure increases inside the damper, and has improved durability and reliability.
This invention concerns a damping force generator for a hydraulic damper comprising a main leaf valve and a sub-leaf valve laminated on each other. The sub-leaf valve closes an opening formed in the main leaf valve and has a lower bending rigidity than that of the main leaf valve. Only the sub-leaf valve opens to generate a damping force when an extension/compression speed of a piston rod is low. Conversely, the main leaf valve opens to suppress increase of damping force when the extension/compression speed of the piston rod is high. An intermediate seat surface is further provided which is formed on the same side of a seat surface which supports the edge of the main leaf valve and supports an inner part of the main leaf valve. Hence, even when the main leaf valve, which is closed, is pushed further in the closing direction by an oil pressure generated in the damper due to extension/compression of the piston rod, the central area of the valve which is most easily bent, is supported by the intermediate seat so that it does not bend. The bending stress acting on the valve is therefore small, the valve is not damaged, and no gap is produced between the main leaf valve and sub-leaf valve.
In another form of the invention, the main leaf valve engages with a piston rod passing through the piston, a port of a connecting passage passing through the piston is formed so as to enclose the piston rod on the underside of the piston, the outer circumferential edge portion of the main leaf valve is supported by an annular seat surface formed on the outer circumferential side of this port, and the intermediate seat surface comprises a plurality of arc-shaped seat surfaces disposed in the vicinity of the approximate mid-point between the annular seat surface and the outer circumference of the piston rod.
In another form of the invention, the main leaf valve engages with a piston rod passing through the piston, a port of a connecting passage passing through the piston is formed so as to enclose the piston rod on the underside of the piston, parts supporting the outer circumferential edge portion of the main valve and parts supporting the approximate mid-point of the main leaf valve are formed alternately and continuously in the seat surface supporting the main leaf valve, and the parts supporting the approximate mid-point of the main leaf valve comprise the intermediate seat surface.
In another form of the invention, a damping force generator for a hydraulic damper comprising a main leaf valve and a sub-leaf valve laminated on each other. The sub-leaf valve closes an opening formed in the main leaf valve and has a lower bending rigidity than that of the main leaf valve, only the sub-leaf valve opens to generate a damping force when an extension/compression speed of a piston rod is low, and the main leaf valve opens to suppress increase of damping force when the extension/compression speed of the piston rod is high. The generator further comprises a seat surface supporting the outer circumference of the main leaf valve, and the outer circumference of the sub-leaf valve extends outwards and near to the point where the outer circumference of the main leaf valve and the seat surface overlap. When the main leaf valve, which is closed, is pushed further in the closing direction by an oil pressure generated in the damper due to extension/compression of the piston rod, the sub-leaf valve extends outwards to the vicinity of the outer circumference supported by the seat surface, and since this sub-leaf valve shares the load with the main leaf valve, deformation of the main leaf valve is suppressed. Hence the bending stress acting on the main leaf valve is small, the main leaf valve is not damaged, and no gap is formed between the main leaf valve and sub-leaf valve.